Many samples of body fluids and the like are separated in a centrifuge to isolate cells or other sediment from the supernatant liquid. It is often desirable to withdraw this heavy sediment for microscopic or other examination. Ordinarily a pipette is used to reach through the supernatant liquid and withdraw a specimen of the sediment in the bottom. Insertion of a pipette can cause mixing of the supernatant liquid and sediment, particularly if there is only a minor density difference. Decantation of the supernatant is nearly impossible and it is desirable to provide a technique for withdrawing sediment from the bottom of a centrifuge tube without disturbing the supernatant.